Self-regulating artificial heart

ABSTRACT

This invention describes a complete artificial heart system which is capable of providing complete self-regulative control of the pumping action of the heart. It comprises a right and left ventricular bladder connected to the blood system. These bladders are housed in right and left ventricular chambers, the space between the bladder and the chamber being filled with a drive fluid. Means are provided for sensing the volume of blood in the right and the left ventricular bladders. There is a power fluid system which comprises a sump maintained at atmospheric pressure, a pump, a flow control means and a switching means. The right and left sensors in the corresponding right and left ventricular chambers have outputs which are functions of the blood volume in the right and left ventricular bladders. A control means takes these sensor outputs and computes two control signals, one of which is a function of the difference between the volumes in the right and the left ventricular bladders, and the other is a function of the sum of the volumes in the right and the left ventricular bladders. The sum function goes to control the rate of flow of the power fluid and the difference function goes to control the switching. The switching means is provided so that when one bladder, for example the right ventricular bladder, becomes fully extended the left ventricular bladder becomes fully compressed, whereupon the drive fluid is switched into the right ventricular chamber to compress the bladder and push its contained blood out into the body system; at the same time, the power fluid that was filling the left chamber is released to flow back to the sump.

United States Patent 1 Bolie 1 SELF-REGULATING ARTIFICIAL HEART [76] Inventor: Victor W. Bolie, 7504 American Heritage Dr., Albuquerque, N. Mex.

[22] Filed: Dec. 23, 1971 [2]] Appl, No.: 211,485

[52] US. Cl 3/1, 3/DIG. 2, 128/1 D, 417/212, 417/216, 417/394 [51] Int. Cl. A611 1/24 [58] Field of Search 3/l, DIG. 2; 128/1 D, DIG. 3; 417/212, 213, 216, 384, 394

[56] References Cited UNITED STATES PATENTS 3,425,064 ,2/1969 Carnevale et al......... 3/1 3,449,767 6/1969 Bolie..;. 3/1 3,491,377 l/1970 Bolie 3/1 3,541,612 11/1970 Carney... 3/1

Primary Examiner-Richard A. Gaudet Assistant Examiner-Ronald L. F rinks Attorney-Head & Johnson [5 7] ABSTRACT This invention describes a complete artificial heart' nected to the blood system. These bladders are housed TO LUNGS [4 1 Jan. 8, 1974 in right and left ventricular chambers, the space between the bladder and the chamber being filled with a drive fluid. Means are provided for sensing the volume of blood in the right and the left ventricular bladders.

sensor outputs and computes two control signals, one

of which is a function of the difference between the volumes in the right and the left ventricular bladders, and the other is a function of the sum of the volumes in the right and the left ventricular bladders. The sum function goes to control the rate of flow of the power fluid and thedifference function goes to control the switching.

The switching means is provided so'that when one bladder, for example the right ventricular bladder, becomes fully extended the left ventricular bladder becomes fully compressed, whereupon the drive fluid isswitched intothe right ventricular chamber to compress the bladder and push its contained blood out into the body system; at the same time, the power fluid that was filling the left chamber is released to flow back to the sump. l f

17 Claims, 23 Drawing Figures TO PERIPHERALS ROM PERIPHERALS LUNGS FLOW CONTROL SUMP PATENTEDJAH 8 m4 SHEET UlUF 15 PATENTEDJAH {H974 3.783.453

sum 02M 15 PATENTEDJAH 81974 sum H UBBF 1s PATENTEDJAH 8 1974 SHEEI GQUF 15 PATENIEUJAN 8 1914 3.783.453 sum osnr 1s PATENTEUJAH 8 1974 SIEH UBBF 15 PATENTEDJAH 8l974 3783.453

sum over 15 TO PERIPHERALS TO LUNGS FROM PERIPHERALS I K i 905 r""- A t 92 1 g (vI \/2)l f(vl vz):

66 707/ I '72 SWITCH PUMP FLOW CONTROL SUMP PATENTED-JAM H974 3.783453 SHE] UBUF 15 PAIENIEIIJAII 8 I974 SIIKET 100T I5 VOLTAGE MOTOR-VOLTAGE AMPLIFIER SPEED CONTROLLED MOTOR BLADDER voLTAGE SUBTRACTOR /25 T I BISTABLE SWITCH FLUID 27 INLET i" 45 DEGREE TORQUE UNIT I I28 I I POSITIVE DISPLACEMENT I EL PUMP II 12/) F BLADDER voLUME SENSOR l 45 DEGREE FOUR PORT vALvE //9 i l I FLUID RETURN PV A0 PATENTEDJAN 8l974 37833153 saw 120F 15 FIG. /20

PATENTEDJAH 8 I974 SHIET 130F 15 F/6. IZE

PATENTEDJAH 81974 SMEI 0F 15 Ill F/G. lZF

SELF-REGULATING ARTIFICIAL HEART BACKGROUND OF THE INVENTION This invention is in the field of artificial hearts. More particularly, it is concerned with a complete system involving two ventricular bladders into which and out of which the blood flows, and including a power fluid sys: tem which is used to alternately compress the two ventricular bladders and further including sensor means to provide feedback signals to control the flow rate and switching of the power fluid so as to produce correct artificial ventricle having a smooth-flow interior, a long fatigue life, a permanently stable bladder-volume coupler, an external contour fitting the inside wall of the self-regulation of the blood flow requirements of the individual at all times.

1 DESCRIPTION OF THE PRIOR ART The need for a reliable and functionally adequate artificial heart has been clearly demonstrated in recent years (see, for example, the publication: Bolie, Victor W., Leading U. S. Artificial Heart Research Programmes, Journal of the Institution of Engineers (India), Voluiri @TNuinberi Part 032,515. 1740,

from each of the two ventricles.

The normal physiological function of the biological heart may be summarized as follows: In the normal 70 kg( 154 lb) adult man the left and right ventricles beat coherently with a pulse rate R which normally is within the range of 72 to 144 strokes/minute. The stroke volume outputs of the two ventricles tend to remain equal, and the right ventricle pumps blood (having low 0 and high CO content) into the pulmonary artery with a stroke volume Q in the range of 70 to 140 milliliters (ml)/stroke. The returning blood (having high 0, and low CO content) from thelungs is pumped into the aorta with a flow rate F QR in therange of 5040 to 20,160 ml/min. Based on the pressure scale of 760 mm Hg 14.7 psi 1,013,200 dynes/cm, thepressure in the pulmonary artery pulsates from zero to about 40 mm Hg above the ambient atmospheric pressure level. The aortic pressure pulsates between 80 mm Hg (diastolic) and 120 mm Hg (systolic) above the ambient atmospheric pressure level existing in the lung alveoli. In older people a blood pressure of 140/90, rather than 120/80, is typical.

A first object of the present invention is to provide an artificial heart which is capable of accommodating wide physiological ranges of blood pressures in the pulmonary artery and in the aorta, and which responds appropriately to physiological changes in the rates of venous blood flow out of the pulmonary and systemic circuits.

A second object of the present invention is to provide adequate feedback control signals from sensors which continuously monitor the instantaneous volumes of the two artificial ventricles.

A third object of this invention is to provide artificial ventricles which are functionally and structurally independent of the particular type of valves used in the blood conduits. i

A fourth object of this invention is to provide a simple mechanical system for converting the instantaneous volumes of the artificial ventricles into appropriate switching and metering control signals for an artificial heart.

rib cage, and an intercostal access tube permitting simple connections for the necessary energizing and monitoring functions. 7

A sixth object of this invention is to provide both a mechanical way and an electrical way of converting the bladder distension signals from an artificial heart into appropriately'timed and metered fluid power pulses.

A seventh object of this invention is to provide a novel mechanism for maintaining constant symmetry and centering of the pulsating bladder in an artificial ventricle while converting the instantaneous bladder volume into an equivalent shaft rotation.

An eighth object of this invention is to provide an artificial heart which gains the several advantages of an unattenuated constant flow of circulating power fluid while still being responsive to physiological demands for moderate changes in cardiac output.

SUMMARY OF THE INVENTION One significant feature of this invention which differs from the prior art systems is that it uses a sensor system which measures the instantaneous volume of fluid in each of two chamber-enclosed ventricular bladders, by

means of which feedback signals are provided to control the power fluid flow in accordance with the requirements of the blood system in the body.

The information produced by the two ventricularbladder-volume sensors is used to produce two control signals, the first control signal which meters the rate of total flow of power fluid, is a function of the sum of the volumes of blood in the two ventricular bladders. The second control signal, which controls the valving or switching of the outflow and return conduits of the power fluid pump with respect to the two ventricular chambers, is a function of the difierence of the two ventricular bladder volumes. The basic artificial heart system thus comprised i fully self-regulating, in that it not only automatically balances the blood outflow rates of the right and left ventricular bladders into the pulmonary artery and the aorta, but also automatically responds to changing physiological requirements in a total blood flow rate. In this invention the mechanical sensors which couple the ventricular bladders to the ventricular chambers is positive, and far more reliable than previous sensors, and have long term durability. Also this system is devoid of the long term base line drifts associated with the gradual slippage of fluid past valves and seals, and with the slow absorption of power fluid gases through the bladder and tubing walls.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and an understanding of the principles of the invention will be evident from the following description, taken in conjunction with the appended drawings, in which: 7

FIG. 1 shows inschematic form the overall generic structure of the blood-interfacingportions of the present invention. I

FIGS. 2A and 2B show structural details of one embodiment of the ventricular sensor mechanisms.

FIGS-3 and 4 show the structures of the metering and switching control devices which are responsive to the sensors and which control the power fluid.

FIGS. 5A and 5B shows the interconnected structures of an impeller pump, a flow attenuator, and a pressure referencing sump.

FIGS. 6A and 6B illustrate the structure of one embodiment of a four-port fluid switching valve.

FIG. 7 shows a graph of the performance characteristics of the pump assembly of FIGS. 5A and 5B.

FIG. 8 shows the characteristic performance curves of the overall artificial heart.

FIG. 9 shows a schematic diagram of the interconnected components of one embodiment of the artificial heart assembly.

FIGS. 10A, 10B and 10C show the structural details of an optimally shaped artificial ventricle which will permit the control and energizing mechanism to be attached from outside the thorax.

FIG. 11 shows a schematic diagram of an electrical embodiment of apparatus for controlling the fluid power pulses applied to a pair of ventricles of the type shown in FIG. 10.

FIGS. 12A, 12B, 12C, 12D, 12E and 12F show various details of an artificial ventricle which has a continuously centered and monitored interior bladder, and is particularly suited to the use of a gas for fluid power.

FIG. 13 shows the design of a physiologically responsive artificial heart which does not require a variable attentuation of the flow rate of the circulating power fluid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the subsequent description, it will be assumed that when the artificial heart of this invention is used to re-v place the biological heart the only portions of the biological heart which remain after excision will be the superior (craniad) remnants of the right and left atrial walls, which can be gathered around and sutured to an appropriate pair of vascular conduits which can carry the returning systemic and pulmonary blood flows into the right and left artificial ventricles, respectively.

Turning now to FIG. 1, which illustrates the basic structure of the blood-interfacing portions of the artificial heart of this invention, it is seen that the fundamental structure is not significantly altered by the particular choice of valves used to insure unidirectional blood flow. 1

In FIG. 1, the right blood conduit 1 is comprised of an inflow orifice 2, an inflow valve 3, an outflow orifice 4, and outflow valve 5, and a right ventricular side-arm 6. Similarly, the left blood conduit 7 is comprised of an 10, an outflow valve 11, and a left ventricular side-arm 12.

In FIG. 1, the complete right ventricle 13 is comprised of an interior right-ventricular bladder 14 enveloped by a rigid right ventricular shell 15, which has a right ventricular side-arm aperture 16 and a right power-fluid aperture 17. Similarly, the complete left ventricle 18 is comprised of an interior left ventricular bladder 19 enveloped by a rigid left ventricular shell 20, which has a left-ventricular side-arm aperture 21 and a left power-fluid aperture 22. It is assumed that the physical shapes of the right and left ventricles 13 and 18 are generally axially symmetric in overall form, ex-

cept for the right and left power-fluid apertures 17 and 22 which extend out of the circumferential surfaces of their respective right and left ventricular shells 15 and 20.

Referring still to FIG. 1 it is seen that the right and left ventricular bladders 14 and 19 are novel in structure in that each has only one moving wall and that this moving wall remains generally perpendicular to the axis of the respective side-arm apertures. Further, it is seen that the right ventricular bladderl4' is provided with a fold-back shoulder 23 which permits simple and positive circumferential scaling to the right ventricular side-arm aperture 16. Similarly, the left ventricular bladder 19 is provided with a fold-back shoulder 26 which permits simple and positive circumferential sealing to the left ventricular side-arm aperture 21. Still further, the moving wall of the right ventricular bladder 14 is provided with a centrally located stiffening disk 24 to which is affixed a linkage-anchoring eyelet 25. The moving wall of the left ventricular bladder 19 is similarly provided with a centrally located stiffening disk 27 to which is affixed a linkage-anchoring eyelet Turning next to FIGS. 2A and 2B, which show the structural details of the ventricular sensing mechanisms, it is seen that the interior medial wall of the right ventricular shell 15 is fitted with a bearing-support strip 29, which supports a protruding right-ventricular front output shaft 30 and a right-ventricular rear output shaft 31. Similarly, theinterior medial wall of the left ventricular shell 20 is fitted with a bearing-support strip 32, which supports a protruding left-ventricular front output shaft 33 and a left-ventricular rear output shaft 34.

In FIGS. 2A and 2B, the right-ventricular front and rear output shafts 30 and 31 are seen to be coupled to the right-ventricular eyelet 25 through the linkage segments 35 and 36, and through the linkage segments 37 and 38, respectively. Similarly, the left-ventricular front and rear output shafts 33 and 34 are seen to be coupled to the left-ventricular eyelet 28 through the linkage segments 39 and 40, and through the linkage segments 41 and 42, respectively.

Referring still to FIGS. 2A and2B, it is seen that the ventricular sensing mechanisms are. designed so that the instantaneous volumes of the right and left ventricular bladders l4 and 19 are converted into equivalent shaft rotations. The arrangement of the various linkages may be conveniently such that the angular rotation of each shaft is confined to a range of plus or minus thirty degrees. Also, it will be seen that the directions of rotation of the front and rear output shafts 30 and 31 of the right ventricle are identical, whereas the front and rear output shafts 33 and 34 of the left ventricle are arranged to rotate in opposite directions.

It will be seen from the illustrations of FIGS. 1 2A and 2B that the structure of the right and left ventricular bladders 14 and 19 are each of a form designed for smooth interiors and long flexion life. Further, it will be seen that the bladder volume sensing mechanisms are designed so that the front and rear output shafts 30, 31, 33, and 34 of the right and left ventricles l3 and 18 rotate freely and thus do not significantly affect the freedom of motion of the respective moving medial walls of the right'and left ventricularbladders 14 and 19.

Turning next to FIG. 3, which shows the structure of the metering control devices, it is seen that the metering control device is comprised of a set of three bellcranks 43, 44 and 45 which are interconnected by an algebraic summing linkage composed of the four link segments 46, 47, 48, and 49. The first and second bellcranks 43 and 44 are pinned to the right and left ventricular front output shafts 3t] and 33, respectively. The third bell-crank 45 is pinned to an output meteringcontrol shaft 50. The lengths of the bell'cranks and their interconnecting link segments in FIG. 3 can be made so that the output shaft 50 rotates through an angular range of plus or minus 45 even though the angu lar rotation of each of the input shafts 30 and 33 is re stricted to a range of plus or minus 30".

Referring now to FIG. 4, which shows the structure of a switching control device, it is seen that the switching control device is in part comprised of a second setof three bell-cranks 51, 52, and 53 which are interconnected by a second algebraic summing linkage composed of the four link segments 54, 55, 56, and 57. The bell-cranks 51 and 52 are pinned to the right and left ventricular rear output shafts 31 and 34. The bell-crank 53 engages a rotary escapement mechanism 58, which has the function of permitting angular rotation of its output shaft 59 only in the forward direction and only .in 90 increments. The stepwise angular rotation of the output shaft 59 is mechanized by the use of two toothed wheels 60 and 61 which are continuously meshed. The toothed wheel 60 is assumed to be under the influence of a continuous forward-acting torque, which may be produced only by any one of a number of suitable devices, such as a small electric motor ora viscous-drag cup emersed in a fluid vortex chamber. The toothed wheel 60 is fitted with a pair of catch-lugs 62 and 63 which are located at opposite ends of a first catch-lug diameter. Similarly, the toothed wheel 61 is fitted with another pair of catch-lugs 64 and 65 which are located at opposite ends of a second catch-lug diameter. The meshed alignment of the first and second toothed wheels 60 and 61 is such that the first catch-lug diameter is horizontal when the second catch-lug diameter is vertical, and vice versa. Further, the bell-crank 53 is shaped so as to engage at one time no more than one of the four catch-lugs 62, 63, 64 and 65. Thus, a backand-fourth rocking motion of the bell-crank 53 results in a series of 90 unidirectional rotations of the output shaft 59. However, it will be seen that a given quarterrevolution of the output shaft 59 will occur only if the angular movement of the bell-crank 53 exceeds a predetermined threshold.

Thus, it will be seen that the designs of the metering and swtiching control devices illustrated in FIGS. 3 and 4 are such that the angular rotation of the output shaft 50 is approximately proportional to the sum of the instantaneous volumes of the right and left ventricular bladders 14 and 19, and that a given quarter-revolution of the output shaft 59 occurs if and only if the magnitude of the algebraic difference between the instantaneous volumes of the right and left ventricular bladders 14 and 19 exceeds a predetermined magnitude.

Attention may now be directed to FIGS. 5A and 5B, which show the interconnected structures of an impel ler pump 66, a flow attenuator 71, and a pressurereferencing sump 68. The power fluid enters the impeller pump 66 through the inlet conduit 69, the pressurereferencing sump 68, and the connection conduit 67. The power fluid leaving the impeller pump 66 flows out of the exit conduit 74 after passing through the connection conduit 70 and the flow attenuator 71.

The pressure-referencingsump 68 has the function of ensuring that the pressure of the power-fluid entering the impeller pump 66 is at all times essentially equal to the ambient atmospheric pressure existing outside the complete power-fluid circuit. The structure of the pressure-referencing sump 68 may thus be simply a segment of pliable tubing of thin rubber or other suitable material.

For reasons which will become a.pparent' later, it will be assumed that the algebraic difference between the maximum volume and the minimum volume of the distensible pressure-referencing sump 68 is at least equal to the sum of the maximum volumes of the right and left ventricular bladders 14 and 19.

As shown in FIGS. 5A and 5B, the flow attenuator 71 may be simply an appropriately housed rotatable vane 72 pinned to a flow-attenuator control shaft 73. The plane of the vane 72 may thus be inclined from the axis of the exit conduit 74 by any desired angle 0:. The least attenuation of the outflow of power fluid from the impeller pump 66 occurs when the angle a is zero. Conversely, the rate of flow of power fluid out of the exit conduit 74 is practically zero when the angle a is equal to ninety degrees. a

In actual operation, the flow-attenuator control shaft 73 in FIG. 5A is made to be a connected extension of the output metering-control shaft 50 in FIG. 3. The direction of rotation of this interconnection is made to be such that the inclination angle a of the flow-attenuator vane 72 decreases in approximate proportion to the sum of the instantaneous volumes of the right and left ventricular bladders 14 and 19. Thus, the outflow of power fluid from the exit conduit 74 is least attenuated when the right and left ventricular bladders 14 and 19 are both maximally distended. Conversely, the outflow of power fluid from the exit conduit 74 is practically zero when the right and left ventricular bladders 14 and 19 are both maximally compressed.

Turning next to FIGS. 6A and 6B, which show the structure of a suitable. four'port fluid-switching valve, it is seen that the structure is essentially that of a rotatable vane centered at the intersection of a pair of perpendicularly crossing power-fluid conduits. The two extending arms 75 and 76 of one of the conduits are fit? ted with suitable output ports 79 and 80. Simi1arly,'the two extending arms 77 and 78 of the other of the two conduits are fitted with suitable input and return ports 81 and 82.

At the center of the intersection of the two powerfluid conduits in FIGS. 6A and 6B, a pair of holes 83 and 84 are 'made in the conduit walls to accommodate a switching-control shaft 85 to which a symmetric vane 86 is pinned. The shape of the four-port valve of FIGS. 6A and 6B is such that the vane 86 may be continuously rotated in a given forward direction. Due to the symmetry of the vane 86, it will be seen that a succession of quarter-revolutions of the switching-control shaft 85 in a given forward direction is equivalent to a movement of 'the vane 86 through an alternating sequence of back-and-forth oscillations of 45 in each direction. Thus, the angle 0 between the plane of the vane 86 and the axis of the extending conduit arms and 76 may be said to remain within the range of from -45 to +45degrees, even if the motion of the shaft is a unidirectional sequence of quarter revolutions. The geometry of the four-port valve of FIGS. 6A and 6B is seen to be such that when 0 +45 the input poi-t8] is connected to the output port 80 and the return port 82 is connected to the output port 79. Conversely, when 45 the input port 81 is connected to the output port 79 and the return port 82 is connected to the output port 80.

In actual operation, the four-port valve of FIGS. 6A and 6B is fluid-coupled to the right and left ventricular shells 15 and 20 of FIG. 1 by connecting the output port 80 to right power-fluid aperture 17 and by connecting the output port 79 to the left power-fluid aperture 22. Also, the four-port valve of FIGS. 6A and 6B is fluid-coupled to the sump-impeller-attenuator assembly of FIGS. 5A and 5B by connecting the valve port 81 to the attenuator exit port 74 and by connecting the valve return port 82 to the sump inlet port 69. Further, the valve switching control shaft 85 is made to be an interconnecting extension of the output shaft 59 of the switching control device of FIG. 4, with the rotational alignment being such that a transition from 6 -45 to 6 +45 can only be triggered when the volume of the right-ventricular bladder 14 is substantially greater than the volume of the left-ventricular bladder 19, and vice versa. In summary, the artificial heart of this invention has a closed power-fluid circuit around which the power fluid flows, first out of the sump and into the impeller, then out of the impeller and into the attenuator, next out of the attenuator and into the valve, then out of the valve to the ventricular chambers and back to the.

valve, and finally out of the valve and into the sump. By means of the valve, the circulating power fluid is caused to alternately compress and dilate the two blood-filled bladders encased by the right and left ventricular shells. The valve has only two operating states, the first of which directs the attenuator outflow into the right shell and concurrently directs the left-shell-outflow into the sump, and the second of which directs the attenuator outflow into the left shell and concurrently directs the right-shell outflow into the sump. The instantaneous volumes V, and V, of the right and left ventricular bladders are continuously sensed by me- V,, Bladder volume difference (V, V,) cm V Bladder volume sum (V, V,) cm V Initial value of V; cm P, Ambient atmospheric pressure dynes/cm P Attenuated impeller output pressure dynes/cm P, Maximum value of boost pressure (P,, P,,) dynes/cm F, Attenuated impeller outflow rate cm lsec F, Maximum value of F, (for P,, P,,) cm lsec Ryg Mean systemic bloodflow return rate cmlsec R Mean pulmonary bloodflow return rate cm lsec P, 7 Mean pulmonary artery backpressure dynes/cm P, Mean systemicarterial backpressure dynes/cm T, Right-systole time constant sec T, Left-systole time constant sec 1-, Duration of right systole sec 1-, Duration of left systole sec 0 Angular osition of four-port valve vane radians K Ratio of V,,/V,',l which triggers 9 switch V Upper limit of V (occurs when 0+45) cm V Lower limit of V (occurs when 0+45) cm V,, Righbsystole volume-sum asymptote cm" V,, Left-systole volume-sum asymptote cm chanical calipers, and their associated sum and difference linkages compute the volume sum V (V, V and the volume difference V (V, V The volume sum V controls the attenuator so that greater flow of power fluid is permitted if V is large. Through an associated escapement device, the volume difference V controls the state of the valve so that a state transition is triggered whenever V exceeds a predetermined positive or negative threshold level. The sump has two functions, the first of which is to ensure that the pressure of the power fluid entering the impeller is at all times equal to the ambient external atmospheric pres- TABLE I DEFINITIONS OF MATHEMATICALTERMS Symbol Definition Dimension V, Right ventricular bladder volume cm V, Left ventricular bladder volume cm V, Bladder maximum stroke volume em and the flow rate F, of the power fluid emerging from the exit conduit 74 of the sump-impeller-attenuator assembly of FIG. 5A. The boost pressure produced by this assembly is (P,, P in which P A is the ambient atmospheric pressure existing in the impeller inlet conduit 67 by reason of the continuous action of the pressure-referencing sump 68. If the attenuator shaft-angle a is set at a 0 for minimum restriction of flow, the relationship between the flow rate'F and the pressure boost (P P is given by a parabolic formula which generally characterizes all impeller pumps, i.e., (P P P -[l (F,/F,,,) in which P, is the maximum boost pressure and F,, is the maximum exit flow rate. Typical values of the parameters P and F,,,, which are essentially determined by the size and speed of the impeller 66, are P,, 8 psi 550,000 dynes/cm and F,, 550 gph 580 em /sec. An impeller pump having these parameters may be obtained commercially as the Model 3-MD chemical magnetic drive pump supplied by the corporation of S. Gelber & Sons of- Chicago, III.

In the more general case, the attenuator shaft angle a of the sump-impeller-attenuator assembly of FIG. 5A

is determined by the sum V, of the right and left ventricular bladder volumes V, and V It is assumed here that V, and V vary within the ranges of 0s V, V,,, and 0 s V, s V,,,, in which the upper-limit volume V may typically have a value of V cm. It is further assumed that when the right and left ventricular bladders l4 and 19 are maximally compressed they will still contain small residual quantities of blood which are not counted in the determinations of V, and V Under the foregoing conditions it will be seen that when the attenuator control shaft 73 of the assembly of FIG. 5A ismechanically coupled to the output shaft 50 of the metering-control device of FIG. 3, the resultant relationshipbetween the exit flow rate F, and the boost pressure (P P of the assembly of FIG. 5A can be approximated by the formula (PR PA) m'l m/ s' l/ m) which is illustrated graphically in FIG. 7 for two different values of V This formula may also be written in the form which will subsequently be used. The next step in the mathematical analysisjs the def, velopmentof th e appropiiateequations for V, and V in which the dot denotes the time rate of change of the 

1. In an artificial heart including a right ventricular bladder and a left ventricular bladder and means adapted to connect said bladders into the blood system of the body in which said heart is to be implanted and including a right ventricular chamber enclosing said right bladder and a left ventricular chamber enclosing said left bladder; the improvement comprising: a. right sensor means to measure a function of the volume V1 of blood in said right bladder, and left sensor means to measure a function of the volume V2 of blood in said left bladder; b. power fluid means; and c. control means responsive to a function of (V1 - V2) for switching the flow of power fluid into one of said chambers, and simultaneously out of the other of said chambers.
 2. The artificial heart as in claim 1 including: control means responsive to a function of (V1 + V2) to control the total flow of said power fluid.
 3. The artificial heart as in claim 1 in which said power fluid means includes sump means maintained at a pressure equal to the ambient atmospheric pressure, and pump means.
 4. The artificial heart as in claim 3 in which said pump means is an impeller pump.
 5. The artificial heart as in claim 3 in which said pump is a positive displacement pump.
 6. The artificial heart as in claim 1 in which said right and left sensor means comprise displacement sensor means respectively respOnsive to a function of the instantaneous volumes of said right and left ventricular bladders.
 7. The artificial heart as in claim 6 in which said sensor means are mechanical means.
 8. The artificial heart as in claim 2 in which the control of the total flow of said power fluid is by means of a flow attenuator.
 9. The artificial heart as in claim 2 in which said total flow control is by means of a variable speed motor which drives said pump.
 10. The artificial heart as in claim 1 in which said ventricular bladder has only one moving wall, and said sensor means measures a function of the displacement of the bladder wall with respect to the chamber wall.
 11. The artificial heart as in claim 1 in which said ventricular bladders each comprise a flattened spheroid of revolution, and including means to ensure that both walls move symmetrically as blood flows into and out of said bladders.
 12. The artificial heart as in claim 3 in which said means for switching the flow of power fluid comprises a four-port valve means in which one port is connected to said pump means, one port to said sump means, one port to said right ventricular chamber and one port to said left ventricular chamber.
 13. In an artificial heart including a right ventricular bladder and a left ventricular bladder and means adapted to connect said bladders into the blood system of the body in which said heart is to be implanted, and including a right ventricular chamber enclosing said right bladder and a left ventricular chamber enclosing said left bladder, the improvement comprising: a. right mechanical sensor means to measure a function of the volume V1 of blood in said right bladder, and means to convert the indications of said right mechanical sensor to electrical signals, ER; b. left mechanical sensor means to measure a function of the volume V2 of blood in said left bladder, and means to convert the indications of said left mechanical sensor to electrical signals, EL; c. fluid power means including sump means and positive displacement pump means; d. variable speed motor means responsive to a function of ER + EL and means to couple said motor to said pump; and e. four-port valve means responsive to a function of ER - EL to control the flow of power fluid into one of said chambers, and simultaneously out of the other of said chambers.
 14. The artificial heart as in claim 13 in which said four-port valve means comprises a two-position valve, which in a first position passes power fluid into a first chamber and out of a second chamber, and in a second position passes power fluid into the second chamber and out of the first chamber.
 15. In an artificial heart including a right ventricular bladder and a left ventricular bladder and means adapted to connect said bladders into the blood system of the body in which said heart is to be implanted, and including a right ventricular chamber enclosing said right bladder and a left ventricular chamber enclosing said left bladder, the improvement comprising: a. right mechanical sensor means to measure a function of the volume V1 of blood in said right bladder, and means to convert the indications of said right mechanical sensor to electrical signals, ER ; b. left mechanical sensor means to measure a function of the volume V2 of blood in said left bladder, and means to convert the indications of said left mechanical sensor to electrical signals, EL; c. fluid power means including sump means and constant flow pump means; d. four-port valve means to control the flow of power fluid into one of said chambers, and simultaneously out of the other of said chambers; and e. control means responsive to a function of ER and EL to control said valve means.
 16. An artificial ventricle adapted to fit the interior contour of the rib cage, said ventricle being comprised of a blood condUit and an encasement shell, said blood conduit being a pliable tube of axially varying cross-section of a size to extend around either the right or left lung from a point near the sternum to a point near the spine, the two ends of said blood conduit being valve-fitted cylindrical segments which extend in generally opposite directions from two smoothly flared transitions emerging from a pliable-flattened-discoid chamber whose axis of revolution is adapted to lie in the plane of the nearby rib arch, said encasement shell being of a rigid form which envelops the discoid-chamber and flared-transition portions of said blood conduit, said shell also fitted with a hollow stem which is aligned coaxially with said discoid-chamber axis and which is adapted to extend outwardly through a surgical opening between two adjacent ribs to couple subcutaneously with a suitable fluid-power source, the medial wall of said discoid bladder-chamber being adhesively affixed to the adjacent medial wall of said shell chamber, the lateral wall of said discoid bladder-chamber being movable and fitted with a central stiffening button to which is coupled a thin rod extending distally outward through said power-fluid stem to permit measurement of the instantaneous volume of said bladder chamber by means of a suitably attached linear-motion transducer.
 17. A gas-operable volume-monitored artificial heart comprised of a pliable bladder, a bladder-centering framework, a symmetric caliper, and a rigid encasement shell, said bladder being comprised of a discoidally shaped chamber having two flat-disc walls from which a pair of valve-fitted inlet and outlet conduits of cylindrical cross section extend in parallel in the upward direction, said bladder chamber having several anchoring tabs attached around its semi-circular periphery, the two flat-disk walls of said bladder chamber each being fitted with a central stiffening button, said shell being generally contoured to envelop said bladder chamber and shaped so as to have a downward-extending power-fluid stem as well as a pair of upward-extending orifice-necks which fit around said bladder inlet and outlet conduits, said framework being attached both to said bladder anchoring tabs and to the interior of said enveloping shell so as to keep said bladder centered at all times within said shell, said caliper having its two arms pinned to eyelets attached to said bladder-wall stiffening buttons and having a mechanical structure which assures that said two bladder walls move in opposite directions by equal amounts, said caliper being coupled to a rotatable shaft aligned coaxially within said power-fluid stem, the rotation of said shaft being a measure of the instantaneous volume of said bladder chamber. 